1. Field of the Invention
The invention relates to channel coding in the air interface in telecommunication systems, and specifically to methods used in selecting coding methods.
2. Description of the Related Art
In Release 6 of the third generation partnership project (3GPP), a Flexible Layer One (FLO) based on similar principles that are used in Universal Terrestrial Radio Access Network (UTRAN), is being standardised for the Global System for Mobile communications/Enhanced Data for GSM Evolution (GSM/EDGE) Radio Access Network (GERAN). Instead of having fixed coding schemes in specifications, Flexible Layer One (FLO) provides a framework that allows one or more coding schemes to be defined at call set-up according to the quality of service (QoS) requirements of the service to be supported and expected conditions of the radio channel. In the terms used in 3GPP standards, these coding schemes are referred to as Transport Format Combinations (TFCs).
TFC selection refers to the process of adaptively selecting an appropriate TFC during transmission in order to adapt to changes in the radio environment such as due to fading. It is analogous to the well known ‘link adaptation’ operation used in Adaptive Multi-Rate (AMR) channels.
On the uplink (UL), maximum TFC selection is, according to standard versions current at the time of writing of this patent application, controlled by the network. The network can signal in-band on the downlink (DL) the maximum TFC that shall be used on the uplink. The network is able select the maximum TFC since the network is aware of the UL radio environment. A similar approach has been proposed for the downlink. In a known proposal, presented during TSG-GERAN meeting #21 (23-27 Aug. 2004), TFC selection would be controlled by the mobile station by signalling in-band on the UL, the maximum TFC that shall be used on the DL. Having the mobile station control the TFC selection in the downlink would be a natural choice, as the mobile station is aware of the DL radio environment. This approach is similar to ‘link adaptation’ operation used in AMR.
However, the aforementioned proposal has the drawback of placing additional processing requirements on the mobile station. Further, it would be advantageous to retain control of TFC selection in the network. For these reasons, this proposal was not incorporated in a standard. Consequently, no method exists to perform TFC selection on the downlink direction.